CINÉTICA E MECANISMO DE OXIDAÇÃO DE UM CONCENTRADO DE ESFALERITA
KINETICS AND MECHANISM OF OXIDATION OF A CONCENTRATE OF SPFALERITE
Vitor de Andrade Alvarenga Oliveira, José Márcio Soares Penna, Lucas Sanches Magalhães
Resumo
A oxidação do concentrado de esfalerita (ZnS) por oxigênio gasoso foi realizada por meio de análise termogravimétrica (TGA). Os produtos de oxidação foram analisados por difratometria de raios X e microscopia eletrônica de varredura (MEV/EDS) e a formação de sulfato de zinco foi detectada durante o processo de oxidação. A pirita presente no concentrado foi aquecida a uma temperatura mais baixa do que a esfalerita e o mecanismo de oxidação estava de acordo com o mecanismo proposto por Dunn J. G. et. al. (1989). A cinética da oxidação da esfalerita foi avaliada por meio do método de isoconversão de Linhas de Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) e não-linear (MNL) e os resultados sugerem que o processo de oxidação segue um mecanismo complexo. Os valores de energia de ativação encontrados foram superiores a 40kJ/mol na gama completa de conversão sugerindo que a etapa de controle ocorre por meio de reação química.
Palavras-chave
Abstract
The oxidation of sphalerite (ZnS) concentrate by gaseous oxygen was carried out by means of thermogravimetric analysis (TGA). The products of oxidation were analyzed by X-ray difractometry and microscopy electronic scanning (MEV/EDS) and the formation of zinc sulphate was detected during the oxidation process. The pyrite present on concentrate was roasted at lower temperature than sphalerite and the mechanism of oxidation was in agreement with the mechanism proposed by Dunn J. G. et. al. (1989). The kinetics of sphalerite oxidation was evaluated by mean of Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS) and nonlinear (MNL) isoconversional method and the results suggest that the oxidation process follow a complex mechanism. The values of activation energy founded were higher than 40kJ/mol at full range of conversion and suggest that the controlling step takes place via chemical reaction.
Keywords
References
1 Dimitrov RI, Moldovanskab N, Bonevc IK, Zivkovicd Z. Oxidation of marmatite. Thermochimica Acta. 2000;362:145-151.
2 Nicolov S, Boyanov B, Moldovanska N, Dimitrov R. Mössbauer spectroscopy study on the oxidation of sulfide zinc concentrate rich in marmatite. Thermochimica Acta. 2001;380:37-41.
3 Boyanov BS, Dimitrov RI, Zivcovic CD. Thermal behaviour of low-quality zinc sulphide concentrate. Thermochimica Acta. 1997;296:123-128.
4 Dunn JG. The oxidation of sulphide minerals. Thermochimica Acta. 1997;300:127-139.
5 Dunn JG, O’Connor BH. The effect of experimental variables on the mechanism of the oxidation of pyrite: Part 2. Oxidation of particles of size 90–125 µm. Thermochimica Acta. 1989;155:135-149.
6 Dimitrov RI, Bonev I. Mechanism of zinc sulphide oxidation. Thermochimica Acta. 1986;106:9-25.
7 Iliyas I, Hawboldt K, Khan F. Advanced kinetics for calorimetric techniques and thermal stability screening of sulfide minerals. Thermochimica Acta. 2010;50:35-45.
8 Vyazovkin S. Handbook of thermal analysis and calorimetry. In: Parameshwaran R, Sarı A , Jalaiah N, Karunakaran R. Applications of thermal analysis to the study of phase-change materials. Oxford: Elsevier; 2008. p. 503-538.
9 Senum GI, Yang RTJ. Rational approximations of the integral of the Arrhenius function. Journal of Thermal Analysis. 1977;11:445-447.
10 Vyazovkin S, Dollimore DJ. Linear and nonlinear procedures in isoconversional computations of the activation energy of nonisothermal reactions in solids. Chemical Information and Computer Science. 1996;36:42-45.
11 Vyazovkin S. A unified approach to kinetic processing of nonisothermal data. International Journal of Chemical Kinetics. 1996;28:95-101.
12 Levenspiel O. Chemical reaction engineering. 3rd ed. New York: John Wiley & Sons; 1999 [citado em 2018 janeiro 16]. Disponível em: https://4lfonsina.files.wordpress.com/2012/11/levenspiel-chemical-reaction-engineering.pdf
13 Vyazovkin S, Burnham AK, Criado JM, Maqueda LAP, Popescu C, Sbirrazzuoli N. ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data. Thermochimica Acta. 2011;520:1-19.
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